With development of information equipment, the needs for low-powder and thin display apparatuses have grown, so that extensive study and development have been made on display apparatus fitted to these needs.
Particularly, such a display apparatus if frequently used outdoors as a wearable PC (personal computer), an electronic notepad, etc., so that it is desirable that the display apparatus is of power and space saving type. For this reason, e.g., such apparatuses in which a display function of a thin display such as a liquid crystal display and a coordinate input process are integrated and a user can directly input information (data) to be displayed on the display by a pressing operation with a pen or finger have been commercialized.
In these equipments, the user operates the equipments by designating a position with the pen or finger on the display apparatuses. For this reason, in order to detect the position, a transparent sheet for sensing the contact of the user's finger or the pen to detect its contact position is disposed on the display apparatuses in many cases.
As another method, Japanese Laid-Open Patent Application (JP-A) Hei 06-236231 has proposed such a scheme that an electromagnetic induction interaction is caused between a metal coil and is incorporated in a pen and a metal coil provided to a detecting device disposed under a display apparatus, thereby to permit detection of a designated position.
Such a so-called electromagnetic induction-type coordination position detection apparatus is used in combination with a display apparatuses to permit handwriting input with a special-purpose pen. Thus, it can be considered that a wearable PC of power and cost saving type or a paper like display in which a user can take notes is realized.
FIG. 9 is a schematic view showing an embodiment of a conventional display apparatus having a pen input function. The display apparatus includes a display panel P0 for displaying, e.g., an image or a character, an input pen 2 for inputting various pieces of information, and a sensor unit S0 for sensing (detecting) a position of the input pen 2 according to an electromagnetic induction scheme. In the input pen 2, a resonance circuit is disposed, and in the sensor unit S0, a sensor coil is disposed, thus permitting detection of a coordinate position according to the electromagnetic induction scheme. A0 represents a plate-like member and is integrally formed with the display panel P0 in order to maintain a strength of the display panel P0.
As one of display apparatuses of thin and lightweight display type for use in the wearable PC, an electrophoretic display apparatus has been proposed in U.S. Pat. No. 3,612,758.
This electrophoretic display apparatus includes a pair of substrates oppositely disposed with a spacing, an insulating liquid filled in the spacing between the substrates, electrophoretic particles dispersed in the insulating liquid, and a display electrode disposed along each of the substrates at each pixel.
The electrophoretic particles are electrically charged positively or negatively, so that they are adsorbed by either one of the display electrodes (upper and lower electrodes) depending on a polarity of a voltage applied to the display electrodes. For example, by controlling a display state so as to be placed in a state such that the electrophoretic particles are adsorbed by the upper electrode and the color thereof is observed and a state such that the electrophoretic particles are adsorbed by the lower electrode and the color of the insulating liquid is observed, it becomes possible to display various images. Hereinafter, the display apparatus of such a type is referred to as a “vertical movement type display apparatus”.
As another display apparatus, a display apparatus of a horizontal movement type as shown in FIGS. 10(a) and 10(b) has been proposed in JP-A Hei 09-211499.
In the display apparatus of this type, different from the above described vertical movement type display apparatus such that the upper and lower electrodes are disposed to sandwich the insulating liquid, electrodes are arranged on one of a pair of substrates. In an embodiment shown in FIGS. 10(a) and 10(b), a first electrode (common electrode) 44 is disposed between adjacent pixels and a second electrode (pixel electrode) 43 is disposed over the entire pixel display area. The second electrode also functions as a reflection plate for reflecting incident light and is covered with an insulating film so as not to take electric charges away from electrophoretic particles.
In the horizontal movement type display apparatus, the insulating liquid is transparent and as shown in FIG. 10(a), the second electrode 43 is covered with electrophoretic particles 47 to effect black display. Further, as shown in FIG. 10(b), the colored electrophoretic particles are collected to the first electrode 44 located between the adjacent pixels to expose the second electrode 43, thus performing white display. As a result, by controlling a polarity of an applied voltage pixel by pixel, it is possible to display an image.
The electrophoretic display apparatus has a memory characteristic, different from most liquid crystal apparatuses. The power of the display apparatus can be held in an off state when the display operation is kept, so that the display apparatus is advantageous in the case where it is assumed that the display apparatus is used in various environments as in the wearable PC.
When the electrophoretic display apparatus is used as the wearable PC or the paperlike display, it is important that the display portion is flexible, i.e., resistive to bending to some extent. It is possible to provide the flexibility to the substrate by forming the substrate with a plastic film. However, in order to provide such a strength that it is capable of resisting repetitive bending, it can be considered that a thin film of metal such as stainless steel is used as the substrate.
However, when the above described electromagnetic induction type coordination position detection apparatus is mounted to such a display apparatus using the metal substrate, the electroconductive metal substrate is interposed between the position detection device and the pen, so that an electromagnetic field produced from the position detection device and the pen generates eddy-current in the metal substrate. For this reason, there has arisen such a problem that the electromagnetic field is attenuated to worsen a sensitivity for position detection.
Similarly as in a touch panel, it can be also considered that the position detection device is constituted by a transparent member and is disposed at a front surface of the display apparatus. JP-A Hei 08-202487 has proposed an electromagnetic induction type position detection apparatus (digitizer) wherein a plurality of coils comprising transparent substrate and transparent electrode are used in combination and dummy wiring is provided in order to obviate a change in transparent electrode, whereby the change in transmittance of the position detection device is not caused to occur.
However, the position detection device is formed by combining the plurality of coils comprising transparent substrate and transparent electrode or effecting the dummy wiring, so that it has a certain thickness. For this reason, an actual distance between the display surface and the pen contact surface becomes large, whereby parallax is caused. As a result, a user has such a sense that it is difficult to write or there is conformity, considerably different from the case where writing is performed in ordinary paper. Further, light passes through at least a thickness corresponding to two layers of transparent electrode, so that there also arises such a problem that a resultant light amount is decreased to approximately 90% compared with the case where a sensor is not provided at the surface of the display apparatus it varies depending upon the thickness.